FIELD OF THE INVENTION
The invention relates to a calibrating wafer having polymer microspheres which adhere thereto. The invention also relates to a method for the production of a calibrating wafer, in which polymer microspheres are applied to the calibrating wafer.
As is known, semiconductor components (for example integrated circuits essentially made of silicon) are produced under so-called clean room conditions, that is to say in an environment containing the least possible amount of so-called particles (dirt). The existence of the respectively required clean room and process conditions is checked regularly as well as when otherwise required (for example due to a reduction in component quality and/or yield), for example by using instruments to measure surface particles. Special wafers, which are generally referred to as calibrating wafers, are used for calibrating the measuring instruments.
Prior art calibrating wafers are semiconductor wafers having a surface which is provided with polymer microspheres, in a specific number and on a specific scale. The polymer microspheres are applied by using a polymer microsphere dispersion diluted to a specific extent. Calibrating wafers which are produced in that way thus have polymer microspheres in a specific amount, in a specific spatial distribution (on the calibrating wafer) and with a specific size distribution. The production method for those calibrating wafers is very expensive. It is true that the calibrating wafers are stored under clean room conditions between the individual checks of the clean room conditions. Nevertheless, since even under the best clean room conditions which can be achieved technically, there are always still traces of, for example, ammonia, hydrochloric acid, hydrofluoric acid or the like in air, they build up over time (including) on the calibrating wafers, for example in the form of ammonium salts. However, over the course of time, those build-ups interfere with the so-called calibration, the effect of which, in the extreme case, is that calibration is no longer possible.
Although as a rule the build-ups can be cleaned off straightforwardly with water, the polymer microspheres are also removed from the wafers at the same time. They therefore need to be re-applied using the heretofore known very expensive method.